Limb surgery on the human body including knees, knee replacement, fracture repair, as well as similar hand, foot, and ankle surgery require that the joint or limb to be operated upon to be precisely and predictably positioned during such surgery. Optimum positioning requires a large range of positive positioning adjustments to be easily available so that the limb or joint to be treated is initially positioned and thereafter maintained in the desired position. Not only must such selected position be maintainable but also it is very important and often necessary that the limb be released and repositioned on demand during the course of the procedure to ensure optimum access thereby to require a variety of angular relationships for effective surgery.